The disclosed invention relates generally to statistical multiplexers, and particularly is directed to a statistical multiplexer system which allocates bandwidth for asynchronous and synchronous channels on a dynamic basis. That is, bandwidth is allocated to a channel if needed, and if not needed bandwidth is de-allocated.
The prior art includes multiplexers which can be generally grouped into two types.
The first type can be referred to as the conventional type of time division multiplexer (TDM) wherein the composite data link is divided into fixed time slots and each time slot is assigned to a predetermined channel. Each channel has bandwidth regardless of whether such channel needs the assigned bandwidth at all times.
The second type of TDM's can be referred to as statistical multiplexers or intelligent multiplexers wherein data from communications channels are formed into frames for synchronous transmission over a data link. In such multiplexers, frames are also used for control purposes. Accordingly, each frame is formatted to identify its type, the channel it is associated with (if any), the number of bytes of data, if it contains data, and other administrative information. Protocols for the transmission of frames (sometimes referred to as packets) have been developed and include the synchronous Data Lind Control (SDLC) protocol and Recommendation X.25 of the Consultative Committee for International Telephone and Telegraph (CCITT). A data frame is created for a particular channel only when data is to be transmitted, thereby avoiding the dedicated time slots of conventional time division multiplexers.
Prior art asynchronous multiplexers have also been adapted for use with synchronous channels. Such adaptations include protocols for recognizing and buffering synchronous data so that frames may be utilized. A second adaptation involves dedicating time slots for synchronous data, a technique that is analogous to conventionally time division multiplexing frames together with synchronous data.
The prior art multiplexers have considerable disadvantages which the present invention overcomes. The conventional TDM had the disadvantage of inefficient use of the data link inasmuch as time slots are dedicated regardless of whether each channel is utilizing its dedicated time slots. For channels which are communicating for large periods of time, the use of the data link is extremely inefficient. With respect to prior art statistical multiplexers, the technique of interleaving synchronous data with frames utilizes fixed time slots--thus resulting in inefficient use of the data link when the fixed time slots are not utilized to capacity. Buffering of synchronous data into frames is a technique which also adds complexity to the multiplexer design.
It is therefore an object of the invention to provide an improved statistical multiplexer for multiplexing synchronous and asynchronous data channels.
A further object of the disclosed invention is to provide an improved multiplexer wherein bandwidth is allocated on a dynamic basis for synchronous and asynchronous data channels.
Another object of the invention is to provide an improved multiplexer for synchronous data channels wherein synchronous channel data is not buffered into frames.
A further object of the invention is to improve statistical multiplexers and provide the dynamic multiplexing of asynchronous and synchronous data channels in such a manner that the statistical multiplexers are transparent to the synchronous channel data.